The invention relates to a turbine ring assembly for a turbine engine, which assembly comprises a plurality of single-piece ring sectors made of ceramic matrix composite material together with a ring support structure.
The field of application of the invention lies in particular in gas turbine aeroengines. Nevertheless, the invention is applicable to other turbine engines, e.g. industrial turbines.
Ceramic matrix composite (CMC) materials are known for their good mechanical properties, which makes them suitable for constituting structural elements, and for their ability to conserve those properties at high temperatures.
In gas turbine aeroengines, improving efficiency and reducing polluting emissions lead to seeking to operate at ever higher temperatures. In turbine ring assemblies that are made entirely out of metal, it is necessary to cool all of the elements of the assembly, and in particular the turbine ring, which is subjected to high-temperature streams. Such cooling has a significant impact on the performance of the engine since the cooling stream is taken from the main stream through the engine. In addition, the use of metal for the turbine ring limits potential for increasing temperature in the turbine, even though that would make it possible to improve the performance of aeroengines.
The use of CMCs for various hot portions of such engines has already been envisaged, particularly since CMCs present density that is lower than that of the refractory metals that are conventionally used.
Thus, making single-piece turbine ring sectors out of CMC is described in particular in Document US 2012/0027572. The ring sectors comprise an annular base having an inner face defining the inside face of the turbine ring and an outer face from which there extend two tab-forming portions having their ends engaged in housings of a metal structure of the ring support.
The use of CMC ring sectors serves to reduce significantly the amount of ventilation that is needed for cooling the turbine ring. Nevertheless, sealing between the gas flow passage on the inside of the ring sectors and the outside of the ring sectors remains a problem. Specifically, in order to ensure good sealing, it is necessary to be able to ensure good contact between the tabs of the CMC ring sectors and the metal flanges of the ring support structure. Unfortunately, differential expansion between the metal of the ring support structure and the CMC of the ring sectors complicates maintaining sealing between those elements. Thus, in the event of differential expansion and depending on the mounting geometry of the ring sectors on the ring support structure, the flanges of the ring support structure might no longer be in contact with the tabs of the sectors, or on the contrary they might exert stress that is too strong on the tabs of the sectors, which can damage them. In addition, as described in Document US 2012/0027572, holding the ring sectors on the ring support structure requires the use of a clamp of U-shaped section which makes mounting the sectors more complicated and increases the cost of the assembly.
Documents U.S. Pat. Nos. 4,596,116 and 4,087,199 disclose a turbine ring assembly in which the ring sectors are held axially between tabs of a ring support structure. Nevertheless, the solution for attaching the ring sectors disclosed in those documents do not make it possible to prevent the ring sectors from moving or sliding in the radial and circumferential directions of the ring, which can be problematic, in particular in the event of contact between the tip of a rotating blade and the inside surface of one or more ring sectors.